Thermosensitive copy sheet



United States Patent 3,413,138 THERMOSENSITIVE COPY SHEET Nick Georgalas and Guy J. De] Franco, Brooklyn, and Pashu Adhikary, Nyack, N.Y., and Peter Loewrigkeit, Totowa, N.J., assignors to Interchemical Corporation,

New York, N.Y., a corporation of Ohio No Drawing. Filed Oct. 13, 1965, Ser. No. 495,711 21 Claims. (Cl. 117-36.8)

This invention relates to copy sheets and to a method of making copies therewith. More particularly the invention relates to copy sheets for use in making copies by a thermographic technique wherein the image on the copy sheet is the result of a chemical change produced by localized heating in the image area.

In recent years thermographic copying of typed or printed originals has become increasingly popular. Thermographic copying involves placing the original in heat conductive relationship with a sheet of copy paper and then subjecting the original and copy sheet to intense irradiation of such character that the printed or typed matter on the original absorbs at least a portion of the radiant energy thereby converting it into heat which causes the image of the original to be developed in the copy sheet. In such a process, it is apparent that the copy sheet must be constructed in such a manner as to be capable of changing to a contrasting color when heated. The thermographic copying process machines for carrying out the process and certain types of heat sensitive papers are described in numerous prior art patents, for instance, United States Patents 2,663,654-7, 2,710,263, 2,740,896.

The heat induced image may be formed either by a physical change in the copy sheet or by a chemical reaction induced by the heat. This invention is concerned with heat-sensitive sheets in which the image is formed as a result of a chemical reaction.

The sheets of this invention are an improvement of the sheets described in copending application S.N. 338,016, Lazzarini et al., now abandoned, which is directed to copying sheets coated with a film-forming binder having dispersed therein any of the heterocyclic derivatives of bis(pdialkylaminoaryl) methane described in U.S. Patent No. 2,981,738 and also having dispersed therein gallic acid as well as other acidic electron acceptors.

It is the principal object of this invention to provide thermographic copying sheets which are even more stable under high humidity conditions for long periods of time than are the thermographic copying sheets of said copending application.

This is accomplished by using sheets with coatings in which the heterocyclic derivatives of bis(p-dialkylaminoaryl) methane of US. Patent No. 2,981,738 in film-forming binders are combined with copolymers of alpha-beta unsaturated carboxylic acids and at least one other ethylenically unsaturated monomer. The gallic acid or other electron acceptors used in the compositions of the copending applications are eliminated from the present compositions. While the components may be used combined in a single coating, it has been found to be most preferable to apply the acid-containing copolymer as a first coating over which a second coating comprising the heterocyclic derivatives of bis(p-dialkylaminoaryl) methane dispersed in a film-forming binder is applied.

The coating, preferably, further contains a waxy material which is preferably a fatty amide or fatty amine. Most preferably the material is a fatty diamide, particularly ethylene bis-stearamide. Other fatty diamides such as ethylene bis-oleamide may be substituted for ethylene bisstearamide as may propylene bis-stearamide as well as fatty amides such as stearamide, palmitamide and oleamide.

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Fatty amides is a common term used to designate amides derived from the higher molecular weight saturated and unsaturated fatty acids; that is they are aliphatic amides, the alkyl groups of which are straight chain or normal groups having from 11 to 21 carbons.

We have further found that fatty amines may be substituted for the waxy amides as may derivatives of these fatty amines such as salts of the fatty amines particularly acetate salts, e.g., the acetate salts of palmityl amine, stearyl amine and oleyl amine. Other waxy derivatives of fatty amines which may be used are those sold under the trademark, Ethomeen. They are tertiary amines having one alkyl group of from 12 to 18 carbons and two oxyethylene, preferably polyoxyethylene, groups attached to the nitrogen, e.g., bis(2-hydroxyethyl) stearyl amine. Fatty amines is also a common term used to designate amines derived from the higher molecular weight saturated and unsaturated fatty acids. They are aliphatic amines, the alkyl groups of which are straight chain or normal groups having from 12 to 22 carbons e.g., primary amines including myristyl amine, pentadecyl amine, palmityl amine, margaryl amine, stearyl amine, myristoleyl amine, palmitoleyl amine, oleyl amine and linoleyl amine, secondary amines of the types in which R may be a C to C alkyl group and tertiary amines such as distearyl methyl amine.

Where the two-coating combination is used the fatty amides or amines are not required but preferred. However, if a single coating system is used, a waxy material such as fatty amide or amine is necessary.

The heterocyclic derivatives of bis(p-dialkylaminoaryl) methane compounds set forth in US. Patent No. 2,981,- 738, are bis(p-dialkylaminoaryl) methanes in which .a heteronitrogen atom of a nitrogen-containing unsaturated heterocyclic nucleus having at least 5 ring members and which is free from carbonyl groups adjacent to the nitrogen atom replaces one of the methane hydrogen atoms. The compounds may be described as N-bis (pdialkylaminoaryl) methyl derivatives of nitrogen-containing unsaturated heterocyclic compounds of said type in which the alkyl groups of the dialkylamino radical each have 1 to 5 carbon atoms and the aryl radicals are mono-nuclear aryl radicals. That is to say, they are heterocyclic derivatives of bis (p-di-lower alkylamino-mono-nuclear aryl) methane in which a heteronitrogen atom, of a nitrogen-containing unsaturated heterocyclic nucleus having at least 5 ring members and which is free from carbonyl and sulfonyl groups adjacent to the nitrogen atom, is linked to the methane carbon atom, the alkyl groups of the dialkylamino radicals each have 1 to 5 carbon atoms, and the aryl radicals are mono-nuclear aryl radicals. The preferred heterocyclic derivatives .are free from both chromophoric groups and from acidic groups containing a hydrogen cation, since such preferred compounds are lightly colored or substantially colorless or colorless in the solid form (leuco form). The alkyl radicals of the p-dialkylamine radicals are lower alkyl radicals, including methyl, ethyl, propyl, butyl and amyl radicals. Compounds in which they are methyl or ethyl are preferred.

The mononuclear aryl radicals include unsubstituted phenylene radicals and phenylene radicals containing one or more inert substituents such .as alkyl, alkoxy, halogen or acylamino substituents; for example, tolylene,methoxyphenylene, chlorophenylene, bromophenylene, etc. Compounds in which they are mononuclear aryl hydrocarbon radicals, and especially phenylene, are preferred.

The nitrogen-containing unsaturated heterocyclic radicals of US. Patent No. 2,981,738 include various types of nitrogen-containing heterocyclic radicals in 'which at least one heteronitrogen atom, which forms the linking point of the radical, is part of a heterocyclic nucleus which contains at least one double bond, at least 5 ring members (and preferably 5 to 6 ring members), and which is free from carbonyl and sulfonyl groups adjacent to said nitrogen atom. Thus, they include unsaturated heterocyclic radicals which contain, besides nitrogen and carbon atoms, oxygen, sulfur and/or additional nitrogen atoms as hetero components. Preferably they contain at least two heteronitrogen atoms, and especially two adjacent heteronitrogen atoms. They also include condensed polynuclear radicals of which one is a nitrogen-containing heterocyclic radical having the said structure; and they include radicals in which hydrogen atoms of the heterocyclic nucleus are replaced by substituent atoms or groups. They are free from chromophoric groups and from acidic groups containing a hydrogen cation. They may, however, contain such substituents as alkyl, aralkyl, hydroalkyl, alkoxy, hydroxyalkoxy, aryl, aroxy, halogen, dialkylamino, acylamino and sulfonamido groups.

The N-bis(p-dialkylaminoaryl) methyl heterocyclic compounds of the patent have the formula wherein R R R and R are each an alkyl radical having 1 to 5 carbon atoms (such .as, methyl, ethyl, propyl, butyl or amyl),

represents a nitrogen-containing heterocyclic radical in which the nitrogen atom which forms the linking point of said radical is part of a heterocyclic nucleus which contains at least one double bond, at least 5 ring members (and preferably 5 to 6 ring members), and which is free from carbonyl and sulfonyl groups adjacent to said nitrogen atom, such as benzotriazolyl, pyrazolyl, imidazolinyl, benzimidazolyl, N-hydroquinolyl, carbazolyl or pyrrolyl radicals, including substituted derivatives of such radicals and preferably those free from chromophoric groups and from acidic groups containing a hydrogen cation, such as the alkyl (e.g. methyl, ethyl, propyl, butyl, 'amyl, hexyl, octyl, dodecyl, hexadecyl, octadecyl or octadocenyl), cycloalkyl (e.g. cyclopentyl, cyclohexyl or methyl cyclohexyl) lalkoxy, hydroxyalkyl, hydroxyalkoxy, fluorine, chlorine, bromine, nitro, aryl, aroxy, dialkylamino, acylamino, sulfamido or condensed cyclic derivatives of the radicals referred to above, and

are selected from the group consisting of the phenylene radical and substituted derivatives thereof, preferably those free from chromophoric groups and from acidic groups containing a hydrogen cation (such as the alkyl,

alkoxy, fluorine, chlorine, bromine, dialkylamino, acylamino or sulfamido derivatives thereof). Examples of such compounds are:

1- [his (p-dimethylaminophenyl) methyl] -benzotriazole 1- [bis (p-dimethylaminophenyl) methyl] -3 ,5 -dimethylpyrazole 1- [bis p-dimethylaminophenyl) methyl] -benzimidazole N- [bis (p-dimethylaminophenyl methyl] -indole,

N- [bis (p-dimethylaminophenyl) methyl] -pyrrole In the preferred two-coating systems, bis(p-dialkylaminoaryDmethanes derivatives are applied over the copolymer coating. The bis(p-dialkylaminoaryl)methane derivatives are applied as a dispersion in a volatile nonpolar organic solvent solution of the film-forming binder.

The compound should be insoluble or at most only very slightly soluble in the solvent. Two solvents which are i1- lustrative of solvents having the desired solubility properties are cyclohexane and heptane.

Any film forming binder may be used. The binder should be soluble in the solvent selected e.g., in a cyclohexane solvent, acrylate resin binder such as polybutylmethacrylate, vinyl toluene-acrylic ester copolymers, cyclized rubber or copolymers of styrene and butadiene may be used as hinders, the latter two being preferred, while in heptane, natural rubber such as cyclized rubber (Pliolite NB), copolymers of butadiene and vinyl toluene, and copolymers of vinyl toluene and acrylates are preferably used as binders and in toluene, polyethylacrylate may be used.

The copolymers used in the first layer are copolymers containing alpha-beta unsaturated carboxylic acid monomers preferably maleic, fumaric, acrylic and methacrylic acids although it-aconic or crotonic acids may be also used for example. These carboxylic monomers may be copolymerized with a wide variety of ethylenically unsaturated monomers. For best results, the unsaturated carboxylic acid component constitutes from 10 to of the total copolymer weight. The olefinically unsaturated monomers which may be copolymerized with the acid monomers include nitriles, such as acrylonitrile and methacrylonitrile; the alkyl esters of acrylic and/ or methacrylic acids such as ethyl hexylacrylate and octyl acrylate but for best results lower alkyl acrylates are preferred (these are defined as the C to 0.; alkyl esters of acrylic and/or methacrylic acids) such as methyl, ethyl, propyl and butyl acrylates as well as methyl methacrylate; alkyl esters of itaconic iacid, particularly lower itaconic esters such as methyl itaconate, butyl itaconate, dimethyl itaconate and dibutyl itaconate and other nitrogen-vinyl polymers such as N-vinyl-2-pyrr0lidone. Vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone and vinyl phenyl ketone, acrolein and methacrolein, amides such as acrylamide, methacrylamide, methylolacrylamide and methylolmethacrylamide; hydroxy compounds such as ethylene glycol monoacrylate and monomethacrylate, propylene glycol monoacrylate .and monomethacrylate, glycerol monoacrylate and monomethacrylate a-nd hydroxyethyl methacrylate; glycidyl acrylate and glycidyl methacrylate; styrene, alphamethyl styrene and the various vinyl toluenes; ethylene glycol dimethacrylate; chloroprene and isoprene; cyclopentadiene and substituted cyclopentadiene such as dihydroxy cyclopentadiene; 2-hydroxymethyl-5-norbornene esters of unsaturated dibasic acids such as dimethyl maleate and dibutyl fumarate; vinyl esters such as vinyl acetate, vinyl propionate and vinyl stearate as well as vinyl chloride; and vinyl alkyl ethers such as vinyl butyl ether, vinyl ethyl ether and vinyl hexyl ether.

The copolymers preferably have molecular weights in the range of from 500 to 8,000 and most preferably from 2,000 to 4,000.

It should be noted that in the present specification and claims all proportions are by weight unless otherwise stated.

Whether a single coating system or a double coating system is used, it is preferable that from 0.3 to 4.1 parts and most preferably from 0.4 to 2.0 parts of the bis(pdialkylaminoaryl) methane are present for each part of the acid monomer present in the copolymer.

In the coating, preferably from 0.1 to 0.6 part of filmforming binder are used for each part of the bis(p-dialkylaminoaryl) methane. Where waxy amide or amine is used, it preferably constitutes from 5 to 20% of the whole dry coating by weight.

The following examples will illustrate the practice of this invention:

Example 1 A solution of 25 parts of a copolymer of 60% styrene and 40% acrylic acid having a molecular weight of about 3,500 dissolved in parts of methyl ethyl ketone is ing of 6 styrene units for each butadiene unit) 2.0 Ethylene bis-stearamide 2.0 Cyclohexane 50.0

is coated over the'aforementioned coating at a thickness of from 0.1 to 0.2 mil and permitted to dry at room temperature.

. The coating is uniform, has good adhesion to the paper and excellent abrasion and pressure resistance. When exposed in the Thermo-Fax'Copying Machine by either front or back printing techniques with an original, the sheet produced a clear copy in which the graphic matter is dark blue, giving good contrast against the background. This excellent contrast does not change even on standing for prolonged periods of time upon conditions of high humidity.

Example 2 Example 1 is repeated using the same ingredients, proportions, conditions and procedure except that another bis(pdimethylaminophenyl) compound is substituted, N- [bis(p-dimethylaminophenyl)methyl] --9 carbazole 1 in place of that of Example 1. The resulting coated paper has all of the desirable properties of that of Example 1, except that the contrast between the dark blue images and the light blue background is not quite as marked as in the coated paper of Example 1.

Example 3 Example 1 is repeated using the same ingredients, proportions, conditions and procedure except that N-[bis(pdimethylaminophenyl)methyl]-indole is used in place of the bis(p-dimethylaminophenyl) compound of Example l. The resulting coated paper has all of the desirable properties of that of- Example 1 except that the contrast between the blue images and the light blue background is not quite as marked as in the coated paper of Example 1.

Example 4 Example 1 is repeated using the same ingredients, proportions, conditions and procedure except that 1-[bis(pdimethylaminophenyl)methyl] 3,5 dimethylpyrazole (made in accordance with Example 2, U.S. Patent No. 2,981,738) is used in place of the bis(p-dimethylaminophenyl) compound of Example 1. The resulting coated paper has all of the desirable properties of that of Example 1.

Example 5 Example 1 is repeated using the same ingredients, proportions, conditions and procedure except that 1-[bis(pdimethylaminophenyl)methyl]-benzimidazole (made in accordance with U.S. Patent No. 2,981,738) is used in place of bis(p-dimethylaminophenyl) compound 'of Example 1. The resulting coated paper has all of the desirable properties of that of Example 1.

Example 6 Example 1 is repeated using the same ingredients, proportions, conditions and procedure except that a copoly- Made in accordance with U.S. Patent No. 2,981,738, Example 6.

rule in accordance with Example 3 of U.S. Patent No. 2,981,738.

' mer of 67% butyl acrylate and 33% acrylic acid having a molecular weight of 4,000 is used in place of the acrylic acid copolymer. The resulting coated paper has all of the desirable properties of that of Example 1.

Example 7 Example 1 is repeated using the same ingredients, proportions, conditions and procedure except that a copolymer of 46% styrene, 41% butyl acrylate and 13% acrylic acid is used in place of the acrylic acid copolymer. The resulting coated paper has all of the desirable properties of that of Example 1.

Example 9 Example 1 is repeated using the same ingredients, proportions, conditions and procedure except that a copolymer of styrene and maleic anhydride in a 1:1 molar ratio and having a molecular weight of 3,000 is used in place of the acrylic acid copolymer. The resulting coated paper has all of the desirable properties of that of Example 1.

Example 10 Example 1 is repeated using the same ingredients, proportions, conditions and procedure except that a copolymer of styrene and fumaric acid in a 1:1 molar ratio and having a molecular weight of 3,000 is used in place of the acrylic acid copolymer. The resulting coated paper has all of the desirable properties of that of Example 1.

Example 11 Example 1 is repeated using the same ingredients, proportions, conditions and procedures except that a copolymer of 53% of vinyl toluene and 47% acrylic acid is used in place of the acrylic acid copolymer. The resulting coated paper has all of the desirable properties of that of Example 1.

Example 12 Example 1 is repeated using the same ingredients, proportions, conditions and procedure except that a copolymer of 24% vinyl toluene, 38% 2-ethylhexyl acrylate and 38% acrylic acid is used in place of the acrylic acid copolymer. The resulting coated paper has all of the desirable properties of that of Example 1.

Example 13 Example 1 is repeated using the same procedure, ingredients and proportions except that the following composition is used in place of the upper coating composition of Example 1:

Parts by weight 1-[bis(p-dimethylaminophenyl)methyl]- benzotriazole 5.0 Ethylene bis-stearamide 2.5 Pliolite N.R. (cyclized rubber) 2.5 Heptane 36.0

The resulting copying sheet has all of the desirable properties of the sheet of Example 1.

Example 14 Example 13 is repeated except that in place of heptane, there is used cyclohexane. The resulting copying sheet has all of the desirable properties of that of Example 13.

Example 15 Example 1 is repeated using the same procedure,

1 ingredients and proportions except that the following composition is used in place of the upper coating composition of Example 1:

Parts by weight 1 [bis(p dimethylaminophenyl)methyl]-benzotriazole 5.0 Ethylene bis-stearamide 2.0

Dow PS-2 (polystyrene having a molecular weight of 22,000) Cyclohexane 36.0

The resulting copying sheet has all of the desirable properties of that of Example 1.

Example 16 stearamide stearyl amine dilauryl amine distearyl amine distearyl methylamine Armeen TD 1 Armeen 2HT 2 Armac 18D 3 Armac HT 4 Ethomeen 18/ 12 5 Armeen TD-A mixture of fatty amines consisting, of 3% myristyl amine, 0.5% pentadecyl amine, 29.5% palmityl amine, 1% margaryl amine, 23.5% stearyl amine, 1% myristoleyl amine, 3% palmitoleyl amine, 37% oleyl amine and 1.5% linoleyl amine.

Armeen 2HTA mixture of fatty secondary amines, the diarnines of hydrogenated tallow consisting of a mixture of amines of the structure RNR, in which 24% of R are stearyl groups.

Armac 18D-A mixture of acetate salts of fatty amines having the structure in which 7% of R are palmityl groups, 90% of R are stearyl groups and 3% of R are oleyl groups.

Armac HTA mixture of acetate salts of fatty amines of the above structure in which 25% of R are palmityl groups, 72% of R are stearyl groups and 3% of R are oleyl groups.

5 Ethomeen 18/12The tertiary amine havlng an alkyl group derived from stearyl amine and two moles of ethylene oxide with an average molecular weight of 362.

Example 17 The following mixture which has been prepared by milling for about 15 minutes:

Parts by weight 1 [bis(p dimethylaminophenyl)methyl]-benzotriazole 6.0 Copolymer made by the addition polymerization of 1 mole of styrene per mole of acrylic acid (in a finely divided state) 10.0 Pliolite S5-E (Styrene-Butadiene copolymer consisting of 6 styrene units for each butadiene unit)--- 3.0 Ethylene bis-stearamide 2.0 Cyclohexane 50.0

is then coated onto a sheet of 11 lbs. white rag paper at a thickness of 0.1 to 0.2 mil. The sheet is then dried by evaporating the solvent. The resulting copying sheet has all of the desirable properties of the sheet of Example 1 except that the stability of the sheet for prolonged periods of time under conditions of high humidity, while being very good, is not quite as good as the sheet of Example 1.

Example 18 Example 1 is repeated using the same ingredients, proportions, conditions and procedure except that ethylene bis-oleamide is used in place of ethylene bis-stearamide.

The resulting coated paper has all of the desirable properties of that of Example 1.

While there have been described what is at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed to cover all such changes and modifications as fall within the true spirit and scope of the invention.

We claim: v

1. A heat-sensitive copying sheet adapted, on being placed in heat-conducted relationship with a graphic original having graphic representations highly absorptive of infrared rays and on irradiation of said graphic original with infrared rays, to produce a copy of said graphic original, said copying sheet comprising a base sheet having thereon (l) a first coating comprising a copolymer comprising the addition polymerization product of an alpha-beta unsaturated carboxylic acid selected from the group consisting of acrylic acid, methacrylic acid, fumaric acid and maleic acid and at least one other ethylenically unsaturated monomer and (2) a top coating comprising a film-forming binder and a heterocyclic derivative of bis(p-dialkylaminoaryl)methane having the formula where R R R and R are individually selected from the group consisting of alkyl radicals having 1 to 5 carbon atoms,

C'D represents a nitrogen-containing heterocyclic radical in which the nitrogen atom which forms the linking point of said radical to the methane carbon atom is part of a heterocyclic nucleus which contains at least one double bond, 5 to 6 ring members, and 1 to 3 nitrogen atoms; said nitrogen-containing heterocyclic radical being selected from the group consisting of those which are free from substituents and those which contain 1 to 2 substituents selected from the group consisting of alkyl up to 18 carbon atoms; octadecenyl; cycloalkyl in which the ring contains 5 to 6 carbon atoms; lower alkyloxy; lower hydroxyalkyl; lower hydroxyalkoxy; phenyl-lower-alkyl; mononuclear hydrocarbon aryl; mononuclear hydrocarbon aroxy; benzo; fluorine; chlorine; bromine; nitro; dilower alkylamino; lower alkanoylamino and -SO NH and @and are selected from the group consisting of the unsubstituted phenylene radical and the phenylene radical monosubstituted by a member of the group consisting of lower alkyl, lower alkoxy, fluorine, chlorine, bromine, di-lower alkylamino, lower alkanoylamino and -SO NH 2. The copying sheet of claim 1 wherein the top coating further includes a waxy material selected from the group consisting of amines and amides of fatty acids having at least 12 carbons.

3. The copying sheet of claim 2 wherein the Waxy material is ethylene bis-oleamide.

4. The copy sheet of claim 2 wherein the waxy material is ethylene bis-stearamide.

5. The copying sheet of claim 4, wherein said heterocyclic derivative of bis(p-dialkylarninoaryl)methane is 1-[bis(p-dimethylaminophenyl)methyl] 3,5 dimethylpyrazole.

6. The copying sheet of claim 4, wherein said heterocyclic derivative of bis(p-dialkylaminoaryl)-methane is 1-[bis(p-dimethylaminophenyl)methyl]-benzimidazole.

7. The copying sheet of claim 4, wherein said heterocyclic derivative of bis(p-dialkylaminoaryl)-methane is N [bis p-dimethylaminophenyl) methyl] -indole.

8. The copying sheet of claim 4, wherein said heterocyclic derivative of bis(pdialkylaminoaryl)-methane is N-[bis(p-dimethylaminophenyl)methyl]-9-carbazo1e.

9. The copying sheet of claim 4, wherein said heterocyclic derivative of bis(p-dialkylaminoaryl)-methane is his (p-dimethylaminophenyl)methane in which one hydrogen atom of the methane carbon atom is unsubstituted and the other hydrogen atom is substituted by a heterocyclic radical which consists of carbon atoms, hydrogen atoms, and three nitrogen atoms, said nitrogen atoms being part of a heterocyclic ring which contains at least one double bond and 5 ring members, the other ring members being carbon atoms, and one of said nitrogen atoms forming the linking point of said radical to the methane carbon atom.

10. The copying sheet of claim 9, wherein said heterocyclic derivative of bis(p-dialkylaminoaryl)-methane is 1- [bis (p-dimethylaminophenyl methyl] -benzotriazole.

11. The copying sheet of claim 4, wherein said filmforming binder is polystyrene.

12. The copying sheet of claim 4, wherein said film forming binder is a copolymer of styrene and butadiene.

13. The copying sheet of claim 4, wherein said film forming binder is cyclized rubber.

14. The copying sheet of claim 1 wherein said alphabeta unsaturated carboxylic acid is acrylic acid.

15. The copying sheet of claim 1 wherein said alphabeta unsaturated carboxylic acid is methacrylic acid.

16. The copying sheet of claim 1 wherein said alphabeta unsaturated carboxylic acid is maleic acid in the form of its anhydride.

17. The copying sheet of claim 1 wherein said other ethylenically unsaturated monomer is a lower alkyl ester of acrylic acid.

18. The copying sheet of claim 1 wherein said other ethylenically unsaturated monomer is styrene.

19. The copying sheet of claim 16 wherein said other ethylenically unsaturated monomer is styrene.

20. The copying sheet of claim 14 wherein said other ethylenically unsaturated monomer is styrene.

21. A heat-sensitive copying sheet adapted, on being placed in heat-conducted relationship with a graphic original having graphic representations highly absorptive of infrared rays and on irradiation of said graphic original with infrared rays, to produce a copy of said graphic original, said copying sheet comprising a base sheet having thereon a coating comprising (1) a film-forming hinder (2) a copolymer comprising the addition polymerization product of an alpha-beta unsaturated carboxylic acid selected from the group consisting of acrylic acid,

10 methacrylic acid, fumaric acid and maleic acid and at least one other ethylenically unsaturated monomer dispersed in said binder, (3) a heterocyclic derivative of his (p-dialkylaminoaryl)methane having the formula wherein R R R and R are individually selected from the group consisting of alkyl radicals having 1 to 5 carbon atoms,

represents a nitrogen-containing heterocyclic radical in which the nitrogen atom which forms the linking point of said radical to the methane carbon atom is part of a heterocyclic nucleus which contains at least one double bond, 5 to 6 ring members, and 1 to 3 nitrogen atoms; said nitrogen-containing heterocyclic radical being selected from the group consisting of those which are free from substituents and those which contain 1 to 2 substituents selected from the group consisting of alkyl up to 18 carbon atoms; octadecenyl; cycloalkyl in which the ring contains 5 to 6 carbon atoms; lower alkyloxy; lower hydroxyalkyl; lower hydroxyalkoxy; phenyl-lower alkyl; mononuclear hydrocarbon aryl; mononuclear hydrocarbon aroxy; benzo; fluorine; chlorine; bromine; nitro; dilower alkylamino; lower alkanoylamino and -SO NH and are selected from the group consisting of the unsubstituted phenylene radical and the phenylene radical monosubstituted by a member of the group consisting of lower alkyl, lower alkoxy, fluorine, chlorine, bromine, di-lower alkylamino, lower alkanoylamino and SO NH and (4) a waxy material selected from the group consisting of amines and amides of fatty acids having at least 12 carbons.

References Cited UNITED STATES PATENTS 2,981,733 4/1961 Kranz 11736.2 2,981,738 4/1961 Kranz 11736.2 2,983,756 5/1961 Kranz 1l736.2 3,129,109 4/1964 Workman 117-368 3,194,677 7/1965 Schwarz 1l7-36.7

MURRAY KATZ, Primary Examiner. 

1. A HEAT-SENSITIVE COPYING SHEET ADAPTED, ON BEING PLACED IN HEAT-CONDUCTED RELATIONSHIP WITH A GRAPHIC ORIGINAL HAVING GRAPHIC REPRESENTATIONS HIGHLY ABSORPTIVE OF INFRARED RAYS AND ON IRRADIATION OF SAID GRAPHIC ORIGINAL WITH INFRARED RAYS, TO PRODUCE A COPY OF SAID GRAPHIC ORIGINAL, SAID COPYING SHEET COMPRISING A BASE SHEET HAVING THEREON (1) A FIRST COATING COMPRISING A COPOLYMER COMPRISING THE ADDITION POLYMERIZATION PRODUCT OF AN ALPHA-BETA UNSATURATED CARBOXYLIC ACID SELECTED FROM THE GROUP CONSISTING OF ACRYLIC ACID, METHACRYLIC ACID, FUMARIC ACID AND MALEIC ACID AND AT LEAST ONE OTHER ETHYLENICALLY UNSATURATED MONOMER AND (2) A TOP COATING COMPRISING A FILM-FORMING BINDER AND A HETEROCYCLIC DERIVATIVE OF BIS(P-DIALKYLAMINOARYL)METHANE HAVING THE FORMULA 